When I buy an item I don’t know where it goes and I can’t find it?

Any item you purchase is added to the bottom middle of your screen. Between the inventory (left side looks like an open box) and the shop (right side looks like a shopping cart). This is the same location where your level up items appear, chests from missions, boxes from daily tasks all appear. However if you currently have items housed there, whatever you purchase is added to end of line. So you are forced to empty out this area if you want instant access to your purchased items. I hope this helps.